The present invention relates to an overhead projector having a reduced height placement of an inverted projection head. In particular, the overhead projector of the present invention includes a post folding mechanism that allows for ease of storage when the projector is not being used, while reducing the possible damage to optical components.
One type of conventional overhead projector (xe2x80x9cOHPxe2x80x9d) uses a Cooke Triplet projection lens where light passes from a light source through a Fresnel lens below a stage on which a transparent object containing the image to be projected is located. After the light passes through the transparent object, the light passes through the Cooke Triplet projection lens and then is reflected off a folding mirror toward a projection screen. To obtain good image quality, the light from the projection lamp focuses at a stop position in or near the Cooke Triplet projection lens. FIG. 1 shows a conventional OHP having a light source, a main body having a horizontal light transmissive stage, and a projection head assembly suspended above the stage by a post. The head assembly includes the Cooke Triplet projection lens and the folding mirror. In traditional OHPs, the post is pivotally attached to the main body, to allow the head assembly and the post to be folded along the side of the main body for storage or lowering of the profile when not in use. Normally, the height dimension of the head assembly above the stage is larger than the length of the main body, and the head assembly clears the front of the machine easily with room to spare.
As described in the above-mentioned related application xe2x80x9cProjector Having an Inverted Head Optical Arrangement,xe2x80x9d a new optical design allows the projection head assembly to be placed closer to the stage. In an OHP having a traditional pivoting post, a lower positioned head assembly may not clear the main body. Accordingly, a user may not be able to fold the system completely without repositioning the head assembly, resulting in the head assembly colliding with the stage. Repositioning the head assembly every time the post is folded requires added handling and results in changing the focus of the OHP. Failure for the head assembly to clear the stage may damage the optical components.
A need exists for other types of low-profile OHP having the ability to fold easily and safely when not in use.
The present invention relates to an improved overhead projector having a reduced height placement of an inverted head assembly and providing clearance such that the inverted head assembly may be pivotally rotated between a storage position and a display position. When the inverted head is in the storage position, the overhead projector is in the storage mode. When the inverted head is in the display position, the overhead projector is capable of being in the display mode.
In brief summary, in one embodiment, the inventive overhead projector comprises (a) a main body having a stage area, (b) an inverted head assembly, and (c) a post suspending the inverted head assembly over the stage area. The post is pivotally attached to the main body in accordance with equation
Clearance={square root over ((Mxxe2x88x92Px)2+(Myxe2x88x92Py)2)}xe2x88x92{square root over ((Fxxe2x88x92Px)2+(Fyxe2x88x92Py)2)}
and the post is outside the stage area when the OHP is in a display mode.
The main body of the overhead projector includes a light transmissive stage having some type of condenser technology, e.g., a Fresnel-condensing lens or an image reflector, positioned underneath. The light transmissive stage defines the stage area of the overhead projector.
In contrast to conventional projectors, the present invention, in one embodiment, uses an inverted head assembly. In an inverted head assembly, the projection lens is positioned such that after light passes through the transparent object, the light reflects off a folding mirror and then passes through the projection lens towards the projection screen. The mirror folds the light path allowing the inverted head assembly, which includes the folding mirror and the projection lens, to be positioned closer to the stage than a non-inverted head assembly.
A post holds the inverted head assembly over the stage area. The post has connected at one end the inverted head assembly and at the other end is pivotally connected to the main body. When the inverted head assembly is positioned upright so as to be over the stage area, the projector is in an image display position and the post is positioned at one corner of the stage area. When the inverted head assembly is rotated to a position in front of the stage area, the projector is in a storage position. One of the advantages of the present invention is that in that when the inverted head assembly is in the display position and focused, a user does not need to refocus the inverted head assembly when changing from the initial display position to the storage position and back to the display position. Thus, the user does not need to change the inverted head assembly position, e.g., by moving it upward away from the stage area, in order to store the OHP.
In a preferred embodiment, the post has a curved end portion. Illustrative end portions include those that are substantially in an xe2x80x9cLxe2x80x9d or xe2x80x9cSxe2x80x9d shape. One skilled in the art will appreciate that other cured portions designs can be used. Such post designs provide the advantages of reduced height placement of the inverted head assembly, clearance such that the inverted head assembly may be pivotally rotated between a storage position and an image display position, and positioning the post outside the stage area, such as at the corner of the stage, so as to provide unobstructed access to the stage area. The curved end portion can be an integral part of the post or it can be an attachment to the post.
Unobstructed access to the stage area is desirable because it allows for easy interchange of display media. For example, a roller attachment can be used, if desired, allowing a presenter to refresh the projected image surface by rotating new media across the stage area.
The overhead projector of the present invention includes a post folding mechanism that creates a reduced height placement of an inverted head assembly and provides clearance such that the projector assembly may be pivotally rotated between a storage position and an image display position.